The present invention relates to the field of analog to digital conversion apparatus for converting the setting of a potentiometer or like device to a binary word.
Various control applications require apparatus for converting the setting of a potentiometer to a binary word. For example, U.S. Pat. No. 4,097,810 and copending U.S. patent applications Ser. Nos. 925,655 and 935,204 disclose tuning systems for radio receivers including apparatus for converting the setting of a potentiometer to a binary word. The binary word controls the division factor of a programmable counter included in a phase locked loop for generating the receiver's local oscillator signal. The division factor of the programmable counter determines the frequency of the local oscillator signal.
Such tuning systems are advantageous in that while they provide a user with controls with which he is familiar, e.g., the conventional dial type adjustment for a radio receiver, the systems are compatible with digital processing circuitry such as microprocessors. The latter capability permits the addition of many user features such as storage of binary words corresponding to preferred radio stations in a memory for rapid future access. Unfortunately, the stability of such systems is limited by the environmental response and aging characteristics of the analog elements of their conversion portion. Accordingly, it is desirable that the conversion portions of such systems have stabilization provisions.